The present invention relates to a method of controlling a vehicle having a steering wheel and road wheels including a pair of road wheels steerable by turning the steering wheel. More particularly, the present invention relates to a motion control method of an automotive vehicle.
U.S. Pat. No. 4,418,780, issued to Hideo ITO et al. on June 12, 1983 and assigned to Nissan Motor Company Limited to which the present application has been assigned, discloses a method of steering an automotive vehicle for the purpose of improving manoeuverability thereof. According to this known method, a pair of rear wheels are steered such that the ratio of a steered angle of the rear wheels to a steered angle of a pair of front wheels is kept at such a value as to maintain an angle of sideslip at a minimal value, thereby to provide high degree of control and stability. The ratio is determined by the vehicle speed, the vehicle weight exerted to each of the front and rear axles, and the steered angle of the pair of front wheels which are always steered by a steering wheel.
However, since the front wheels are steered through an angle which is proportioned to an angle through which the steering wheel is manually turned at a ratio which is a constant for a given turned angle of the steering wheel, whereas the rear wheels are steered through an angle which is proportioned to the steered angle of the front wheels at a ratio which varies in response to the vehicle speed, the known method gives a characteristic curve as shown in FIG. 1 that at low vehicle speeds, the rear wheels are steered in the opposite direction, while, at high vehicle speeds, the rear wheels are steered in the same direction as the front wheels are steered. Although, according to this known method, the vehicle can be steered with excellent control and stability at any vehicle speed, those skilled in the art have encountered a problem that is attributed to the fact that the steering characteristic of the front wheels and thus that of the rear wheels are fixed and determined by predetermined functions, respectively, regardless of a difference in driver's habit or technique in steering the vehicle. The problem is that it is impossible to vary the control characteristics of a vehicle with a variation in a driver's habit or technique in manipulating a steering wheel or his taste in control response of the vehicle to the manipulation of the steering wheel. Manufacturing various different types of vehicles which fit well with different driver's tastes would require a large fleet of vehicles with many different specifications, thus raising manufacturing cost of each unit. If the same driver continues to use the same vehicle, the above mentioned solution will work. But, it will not do so if the same vehicle is used by different drivers having different tastes.